A polymer alloy system of polycarbonate resin and styrene has been widely used in many fields such as home electric appliances or automobiles due to its excellent mechanical properties such as rigidity and impact resistance, and also its excellent fluidity, heat resistance, electrical properties, and dimensional stability. In recent years, in view of reducing weight, articles or parts with still thinner walls are requested, so that the material used for these articles or parts is required to have an improved fluidity.
Polycarbonate resin is self-extinguishing by itself, but its flame retardance is lowered by alloying. When polycarbonate resin is used as a material for OA, telecommunication, or electric and electrical instruments, the flame retardance of polycarbonate resin is required to be leveled up to ensure still higher safety.
In the polymer alloy system of polycarbonate resin and styrene, fluidity is generally improved by increasing the content of styrene resin or by decreasing the molecular weight of polycarbonate resin. However, increase in styrene resin content leads to lowering in surface impact strength and also in flame retardance. Decreasing in the molecular weight of polycarbonate resin leads to lowering in Izod impact strength and elongation. Thus, it is rather difficult to get good balance between these properties and fluidity.
A method of adding a plasticizer to polycarbonate resin is an older method for improving fluidity of polycarbonate resin (referred to, for example, Patent Document 1). A phosphoric acid ester has been used as a plasticizer for a polycarbonate-based material and is known to provide relatively good balance between fluidity and impact resistance, and also provide flame retardance. However, phosphoric acid ester added brings such problems of lowering in heat resistance of the material itself, sticking of the material to molds on molding, failures in appearance of molded articles, and lowering in recycling efficiency caused by hydrolysis of polycarbonate resin. In order to solve these problems, a silicone-based material has been developed as a next-generation flame retardant material, but a material having a sufficient fluidity which meets the specification of large-size molded articles has not yet been developed.
Patent Document 1: Japanese Patent Application Publication (JP-B) No. Heisei 7 (1995)-68445